1. Field of the Invention
This invention relates to a multicycle Stirling engine comprising four or more systems of interconnected expansible chambers, each system including one or two expansion chambers and one compression chamber. In each system there is a phase difference between the volume variations of the compression chamber and the volume variations of the expansion chamber which communicate with each other through a conduit with heat exchanging sections. Each system is charged with a compressible operational medium, such as a permanent gas, which is adapted to flow back and forth between the chambers through the above conduit.
If this medium conveys heat from a higher temperature level to a lower temperature level, this medium being heated, for example by a burner and cooled by a coolant, such as water, the Stirling engine is capable of converting heat into mechanical energy, so that the machine performs an engine cycle and operates as a hot gas engine. If on the contrary this medium conveys heat from a lower temperature level to a higher temperature level, for example from a space to be cooled to a coolant, for example water at ambient temperature, the machine is capable of converting mechanical energy or heat energy into cold, so that a refrigerating cycle is performed and the machine acts as a cold gas refrigerator. If the medium simultaneously performs an engine cycle and also a refrigerating cycle, then the machine acts as a heat-operated heat transporting device.
In particular this invention relates to improved means of performing the desired thermodynamic cycles for the operational medium in such devices through compounding of the constituent cycles in a multi-cycle machine, using pairs of double-acting pistons rigidly connected to each other, each of which is in communication with the operational medium of at least four separate thermodynamic cycles.
2. Description of the Prior Art
Single cycle Stirling engines were in common use about one hundred years ago. Although many different types have been made, they have not proved competitive with other thermal machines to continue to be used. Due to the shortcomings of known Stirling cycle machines, they are presently being made only for experimental purposes as engines and only in limited numbers as refrigerators.
Multi-cycle Stirling engines known to the art are more compact and have a higher mechanical efficiency and specific power. However, output from individual pistons is not balanced, and a heavy duty crankshaft or a swashplate is needed to coordinate the pistons and transmit the load. Examples of these are described in the following U.S. Pat. Nos. 2,611,235 to F. L. van Weenen, 2,657,553 to C. O. Jonkers, 2,724,248 to T. Finkelstein, 3,527,049 to V. Bush and 3,538,706 to R. R. Toepel.
Up to about fifteen years ago nearly all Stirling engines had mechanical output delivered from an engine, or supplied to a refrigerator, through a rotating shaft connected to the reciprocating members attached to the pistons at one end and to a rotating crankshaft at the other end. Each of the main reciprocating members of a Stirling engine was therefore linked to the rotating crankshaft and the phase relationship between the reciprocating members was predetermined. One notable exception was U.S. Pat. No. 2,558,481 to A. A. Dros; however since energy flow in this design is not balanced, stable operation was difficult to achieve.
A tuned free-piston single-cycle Stirling engine without such linkage was disclosed by U.S. Pat. No. 3,552,120 to W. T. Beale, but its maximum power is limited to two thousand watts. An engine using bellows and tuned electrical circuits with a resonant mechanical spring-mass system is described in U.S. Pat. No. 3,548,589 to E. H. Cooke-Yarborough. However this is only suitable for powers of up to twenty watts.
Since Stirling engines have the inherent advantage of high efficiency, much research has been done to develop Stirling engines that would be competitive with internal combustion engines. In recent years intensified air pollution problems and increased government pollution controls have also increased research in the field. Yet they are still not commercially produced and no competitive Stirling cycle machine has been developed to date. Engines that were known to prior art with mechanical transmission were complicated, bulky and expensive, while those that used free pistons were limited to single cycles and a low power output. In contrast, the principle disclosed by this invention leads to considerable simplification and increase in performance, as well as reduction in size and cost.